1. Field of the Invention
The present invention relates to a correlation method applicable to a Code Division Multiple Access (CDMA) receiver, and more particularly, to a correlation method and a signal processing method of a CDMA receiver using mapping which can call In-phase (I) and Quadrature-phase (Q) correlation values to be mapped to digital data, in real-time, by using a prepared correlation value mapping table in order to reduce code calculation significantly, thereby enabling high speed processing.
2. Description of the Related Art
In general, a Global Positioning System (GPS) receiver serves to receive time and position information from GPS satellites. The GPS receiver should correctly compensate phase errors of carrier waves and Coarse/Acquisition (C/A) codes based on received signals and predetermined signals in order to correctly acquire the information received in GPS signals.
FIG. 1 is a block diagram illustrating a typical GPS receiver.
Referring to FIG. 1, the GPS receiver includes a Radio Frequency (RF) receiver 10 for receiving GPS signals through an antenna ANT and converting the GPS signals into Intermediate Frequency (IF) signals and a Main Process Unit (MPU) 20 for extracting satellite data from the IF signals received from the RF receiver 10.
As means for acquiring GPS information, the MPU 20 includes a correlator that produces the correlation value between a digital IF signal and a reference signal. Such a correlator will be described with reference to FIG. 2 as follows.
FIG. 2 is a block diagram illustrating a correlator of a GPS receiver of the related art.
As shown in FIG. 2, the correlator of the GPS receiver of the related art includes a carrier wave generator 21, a code generator 22, a carrier mixer 23, an I code mixer 24, a Q code mixer 25, an I integrator 26 and a Q integrator 27. The carrier wave generator 21 generates a carrier wave signal in response to a carrier wave control signal Scar, and the code generator 22 generates a C/A code in response to the code control signal. The carrier mixer 23 divides a digital signal of about 16 MHz into I and Q signals and mixes the I and Q signals with the carrier wave signal from the carrier wave generator 21 to produce I and Q baseband signals of about 2 MHz, respectively. The I code mixer 24 mixes the I baseband signal, from the carrier mixer 23 with the code from the code generator 22 to produce individual I Correlation Value (ICV), and the Q code mixer 24 mixes the Q baseband signal from the carrier mixer 23 with the code from the code generator 22 to produce individual Q Correlation Value (QCV). The I integrator 26 integrates the individual ICV received from the I code mixer 24, and the Q integrator 27 integrates the individual QCV received from the Q code mixer 25.
Here, the I integrator 26 outputs the ICV including an I Prompt (IP) value in the present prompt, an I Early (IE) value in a half-chip early code and an I Late (IL) value in a half-chip late code.
In addition, the Q integrator 27 outputs the QCV including a Q Prompt (QP) value in the present prompt, a Q Early (QE) value in a half-chip early code and a Q Late (QL) value in a half-chip late code.
Since the correlator of the GPS receiver is composed of a hardware, the C/A codes set inside the correlator are different according to terminals and thus the correlators should be realized in different versions according to the terminals.
Accordingly, one type of hardware correlator is not used in different types of terminals, causing a problem of poor applicability.
Although a software correlator can be realized in order to alleviate the problem of the hardware correlator, real-time signal processing is impossible due to massive amount of data to be calculated.